Robust estimation of quantitative perfusion from multi-phase pseudo-continuous arterial spin labeling.

PURPOSE: Multi-phase PCASL has been proposed as a means to achieve accurate perfusion quantification that is robust to imperfect shim in the labeling plane. However, there exists a bias in the estimation process that is a function of noise in the data. In this work, this bias is characterized and then addressed in animal and human data. METHODS: The proposed algorithm to overcome bias uses the initial biased voxel-wise estimate of phase tracking error to cluster regions with different off-resonance phase shifts, from which a high-SNR estimate of regional phase offset is derived. Simulations were used to predict the bias expected at typical SNR. Multi-phase PCASL in 3 rat strains (n = 21) at 9.4 T was considered, along with 20 human subjects previously imaged using ASL at 3 T. The algorithm was extended to include estimation of arterial blood flow velocity. RESULTS: Based on simulations, a perfusion estimation bias of 6-8% was expected using 8-phase data at typical SNR. This bias was eliminated when a high-precision estimate of phase error was available. In the preclinical data, the bias-corrected measure of perfusion (107 ± 14 mL/100g/min) was lower than the standard analysis (116 ± 14 mL/100g/min), corresponding to a mean observed bias across strains of 8.0%. In the human data, bias correction resulted in a 15% decrease in the estimate of perfusion. CONCLUSIONS: Using a retrospective algorithmic approach, it was possible to exploit common information found in multiple voxels within a whole region of the brain, offering superior SNR and thus overcoming the bias in perfusion quantification from multi-phase PCASL.

Repression of cancer cell senescence by PKCι.

Senescence is an irreversible growth arrest phenotype adopted by cells that has a key role in protecting organisms from cancer. There is now considerable interest in therapeutic strategies that reactivate this process to control the growth of cancer cells. Protein kinase-Cι (PKCι) is a member of the atypical PKC family and an important downstream mediator in the phosphoinositide-3-kinase (PI-3-kinase) pathway. PKCι expression was found to be upregulated in a subset of breast cancers and breast cancer cell lines. Activation of the PI-3-kinase pathway by introduction of mutant, oncogenic PIK3CA into breast mammary epithelial cells increased both the expression and activation of PKCι. In breast cancer cells lines overexpressing PKCι, depletion of PKCι increased the number of senescent cells, as assessed by senescence-associated ß-galactosidase, morphology and bromodeoxyuridine incorporation. This phenomenon was not restricted to breast cancer cells, as it was also seen in glioblastoma cells in which PKCι is activated by loss of PTEN. Senescence occurred in the absence of a detectable DNA-damage response, was dependent on p21 and was enhanced by the aurora kinase inhibitor VX-680, suggesting that senescence is triggered by defects in mitosis. Depletion of PKCι had no effect on senescence in normal mammary epithelial cell lines. We conclude that PKCι is overexpressed in a subset of cancers where it functions to suppress premature senescence. This function appears to be restricted to cancer cells and inhibition of PKCι may therefore be an effective way to selectively activate premature senescence in cancer cells.

Noninterference of cytochrome P4501A2 in the cytotoxicity of tacrine using genetically engineered V79 Chinese hamster cells for stable expression of the human or rat isoform and two human hepatocyte cell lines.

Tacrine (THA) is the only drug currently approved for the treatment of Alzheimer's disease. A common side effect of this drug in humans is major hepatotoxicity. THA-induced toxicity may be related to a metabolic pathway implicating cytochrome P450 1A2 (CYP1A2). The purpose of this study was to clarify the role of the metabolic conversion of THA by CYP1A2 in the cytotoxicity of THA. The cytotoxicity of THA was evaluated in two human hepatocyte cell lines, HepG2 and Chang liver, and on the V79 Chinese hamster cell line, which does not express cytochrome P450 activity, and its variants, genetically engineered for expression of human or rat CYP1A2. Cells expressing human CYP1A2 metabolized THA to form its 1-OH derivative (Vmax = 9.36 +/- 0.57 pmol min(-1) mg(-1) total protein), whereas no metabolism was observed with the nonexpressing parental cells. In all cell lines, THA induced a marked decrease in cell viability and a strong inhibition of RNA and protein synthesis. However, these cytotoxic effects did not differ in parental V79 cells and variant cells expressing human or rat CYP1A2. The IC50 were tenfold higher for cell viability than for RNA and protein inhibition after 3 hr of incubation but were similar after 24 hr (P < 0.0001), indicating that this early inhibition was not a transient effect and could lead to cell death. These results strongly suggest that THA-induced cytotoxicity is not mediated by CYP1A2.

Mucoadhesion of hydroxypropylmethacrylate nanoparticles to rat intestinal ileal segments in vitro.

The purpose of this study was to evaluate the adhesion of HPMA nanoparticles to mucus using a perfused rat ileum test system. Radiolabeled nanoparticles were prepared and deposited onto rat ileal segments in vitro. The segments were perfused and the perfusate was collected in fractions and assayed for radioactivity. Between 10 and 50% of the radioactivity was eliminated over the first 120-sec perfusion, whereas the remaining activity was firmly attached to the ileum. Among the variables tested, the time interval between nanoparticle deposition and perfusion played the major role, indicating that the mucus-nanoparticle interaction is likely to result from the diffusion of polymers into the mucus and of mucin into the polymeric matrix.

New method for the preparation of cyanoacrylic nanoparticles with improved colloidal properties.

The purpose of this study was to prepare nanoparticles with a size significantly smaller than 0.1 micron. It was shown that when sulphur dioxide was dissolved in the cyanoacrylic monomer at a high concentration, subsequent anionic polymerization in an aqueous phase produced particles as small as 10 nm. Moreover, the obtained particles displayed an important negative charge which improve their stability against aggregation. Finally, nanoparticles were successfully prepared in double-distilled water, thereby avoiding the use of dextran which can induce anaphylactoid reactions.

Direct continuous measurements of thermal expansion coefficients of liquids and solids using flow microcalorimetry.

A differential heat capacity flow microcalorimeter is used to monitor in a continuous mode the thermal expansion of a sample during a programmed temperature scan. The sample may consist of liquids, suspensions, or bulk solids in a confining liquid and the typical temperature scanning rate is of the order of 1 K/min. The technique has a precision better than 1% and a detection limit of 10(-6) ml s(-1). In contrast to conventional dilatometers, this technique offers variable sensitivity and is not limited by the magnitude of the total volume change during the experiment. Various expansibility data obtained in the temperature range 10-55 degrees C are reported for several systems, namely water, benzene, carbon tetrachloride, and aqueous solutions of sodium chloride. The volume changes for the thermal transition of Teflon and the phase separation of 2-butoxyethanol/water mixtures further illustrate the possibilities of this new technique.